The electrostatic charge buildup on the surface of plastic pipe, and in particular polyethylene pipe, is a hazardous problem when attempting to repair hydrocarbon gas pipelines because of potential spark discharges that may occur. It has been found that the buildup of charge can cause electrical shock to personnel that come in contact with a charged pipeline surface and can trigger a fire and explosion when discharged.
It is common for charge to be generated by triboelectrification (frictional charging). Charge can be stored on the surface of polyethylene pipe because of the inherent high resistivity of the polyethylene pipe. Particles, such as dust and rust, in the gas produce charge at the interior wall of the plastic pipe because of the triboelectrification. Triboelectrification can generate either a positive or a negative charge in the plastic pipe. It has also been observed that charge present inside these pipes induce charge buildup on the outside surface of the pipe.
Because of the presence of these charges, an electrical spark discharge can occur from metal objects or be experienced by personnel near the pipe when attempting to repair the pipe. Technology and procedures have been developed to discharge both the interior and exterior surfaces of polyethylene pipe. For example, in a report entitled "Control of Static Hazard in Plastic Pipe" which was prepared by Battelle (Columbus Laboratories), it was determined that water sprayers were effective for discharging charge on the interior wall of pipes but required access to the interior of the pipe. It was found that water on polyethylene pipe surfaces does not form a continuous wet film. Unfortunately, if the film coating of the fluid is not continuous, complete discharge of the interior surface of the pipe is not effective.
In addition, the above report discloses the use of X-ray as an effective method for discharging static charges on both the interior and exterior walls of pipe. Unfortunately, the use of X-ray is not practical for field applications. Unfortunately, X-ray equipment is cumbersome, expensive and potentially hazardous to operators.
Prior applications did not consider the use of an antistatic fluid in polyethylene pipe by selectively penetrating the pipe and spraying the antistatic fluid in the pipe to discharge the surface. Another problem which has yet to be confronted is the use of an antistatic fluid which will not degrade the integrity of polyethylene pipe. Since polyethylene pipe is a polymer, many common fluids tend to degrade the integrity of the pipe. In addition, since the antistatic fluid would be in the gas stream, it is imperative that the antistatic fluid not create problems in gas processing facilities such as the creation of hydrates or the reduction of the heating value of the gas.
A need has therefore arisen for an apparatus and method for discharging the internal surface of polyethylene pipe which avoids the prior difficulties with antistatic fluids and which is cost effective for use in remote areas.